Because a man is very sensitive after an orgasm, he is very sensitive on his head. So when a woman tries to rub his cock with a dry hand, the man has to try very "hard" to not slap the woman for rubbing his "hat". So The Hard Hat is created.

After my woman whacked me off, she kept trying to find more, but my hat was too sensitive, and I tried very hard not to slap that hoe. The Hard Hat I got last night was gruesome.